IGZO Research Articles

An Integrated Analog Front-End System on Flexible Substrate for the Acquisition of Bio-Potential Signals.

The application of a versatile, low-temperature thin-film transistor (TFT) technology is presently described as the implementation on a flexible substrate of an analog front-end (AFE) system for the acquisition of bio-potential signals. The technology is based on semiconducting amorphous indium-gallium-zinc oxide (IGZO). The AFE system consists of three monolithically integrated constituent components: a bias-filter circuit with a bio-compatible low cut-off frequency of ≈1Hz, a 4-stage differential amplifier offering a large gain-bandwidth product of ≈955kHz, and an additional notch filter exhibiting over 30dB suppression of the power-line noise. Respectively built using conductive IGZO electrodes with thermally induced donor agents and enhancement-mode fluorinated IGZO TFTs with exceptionally low leakage current, both capacitors and resistors with significantly reduced footprints are realized. Defined as the ratio of the gain-bandwidth product of an AFE system to its area, a record-setting figure-of-merit of ≈86kHzmm-2 is achieved. This is about an order of magnitude larger than the < 10kHzmm-2 of the nearest benchmark. Requiring no supplementary off-substrate signal-conditioning components and occupying an area of ≈11mm2 , the stand-alone AFE system is successfully applied to both electromyographyand electrocardiography (ECG).

AWafer-Scale Nanoporous 2D Active Pixel Image Sensor Matrix with High Uniformity, High Sensitivity, and Rapid Switching.

2D transition-metal dichalcogenides (TMDs) havebeen successfully developed as novel ubiquitous optoelectronics owing to their excellent electrical and optical characteristics. However, active-matrix image sensors based on TMDs have limitations owing to the difficulty of fabricating large-area integrated circuitry and achieving high optical sensitivity. Herein, a large-area uniform, highly sensitive, and robust image sensor matrix with active pixels consisting of nanoporous molybdenum disulfide (MoS2 ) phototransistors and indium-gallium-zinc oxide (IGZO) switching transistors is reported. Large-area uniform 4-inch wafer-scale bilayer MoS2 films are synthesized by radio-frequency (RF) magnetron sputtering and sulfurization processes and patterned to be a nanoporous structure consisting of an array of periodic nanopores on the MoS2 surface via block copolymer lithography. Edge exposure on the nanoporous bilayer MoS2 induces the formation of subgap states, which promotes a photogating effect to obtain an exceptionally high photoresponsivity of 5.2 × 104 A W-1 . A 4-inch-wafer-scale image mapping is successively achieved using this active-matrix image sensor by controlling the device sensing and switching states. The high-performance active-matrix image sensor is state-of-the-art in 2D material-based integrated circuitry and pixel image sensor applications.

An Oxide-Based Bilayer ZrO₂/IGZO Memristor for Synaptic Plasticity and Artificial Nociceptor

As artificial intelligence technology advances, memristors are promising to be used as artificial synapses to mimic various biological learning behaviors. In this work, all the memristors are fabricated using 45-nm complementary metal–oxide–semiconductor (CMOS) technology on Si/SiO2 substrate. By inserting a 3-nm indium gallium zinc oxide (IGZO) layer into the Pt/ZrO2/TiN single-layer (SL) memristor, the storage window of the bilayer (BL) memristor is enhanced to 11 times that of the single one. It demonstrates the multilevel conductivity modulating properties of the BL memristors, which can be used to mimic the learning behavior of biological synapses. The Pt/ZrO2/IGZO/TiN memristor has achieved synaptic plasticity, including long-term potentiation/depression (LTP/LTD), spike-timing-dependent plasticity (STDP), and paired-pulse facilitation (PPF). Moreover, the inadaptation, threshold, hyperalgesia, and allodynia characteristics of a nociceptor based on Pt/ZrO2/IGZO/TiN memristor have been accomplished. The BL oxide-based memristor with outstanding synaptic properties and the simulation as an artificial nociceptor provides a feasible application in the future neuromorphic systems for bionic robots.

Thermal shape morphing of membrane-type electronics based on plastic-elastomer frameworks for 3D electronics with various Gaussian curvatures

This study demonstrates a means of shape morphing planar membrane-type electronic devices into three-dimensional (3D) structures with various Gaussian curvatures using a plastic-elastomer supportive framework consisting of acrylonitrile–butadienestyrene (ABS) lines with tensile stress inside an Ecoflex film. The plastic part, created by extrusion shear printing (ESP), provides the driving force for shape morphing upon thermal annealing, whereas the elastomer part provides a base to mount membrane-type electronic devices and allows a comparably large degree of deformation. To ensure reliable interfacial adhesion in the plastic-elastomer framework, the ABS lines are treated with an allyl-terminated self-assembled monolayer (SAM) for chemical bonding to the Ecoflex layer. To determine control parameters for reliable shape morphing, the annealing conditions (e.g., temperature and time), the printing conditions (e.g., shear rate and pitch), and relative thicknesses of the ABS/Ecoflex are examined. Based on these findings, various 3D structures, including bent, cone, saddle, and dome shapes, can be generated from planar forms using ABS-Ecoflex frameworks, which are also predicted by a mechanical finite element method (FEM) simulation. Furthermore, a metal electrode and a membrane-type indium gallium zinc oxide (IGZO) transistor array are successfully mounted on ABS-Ecoflex frameworks and transformed into curvilinear structures without electrical failure.

Dependence of the Transfer Characteristics of Metal-Oxide Thin-Film Transistors on the Temperature of an Extended Oxidizing Heat-Treatment

When a metal-oxide (MO) thin-film transistor (TFT), specifically that based on indium-gallium-zinc oxide (IGZO), is subjected to an oxidizing heat-treatment, its transfer characteristic is found to exhibit a parallel shift that depends on the temperature and saturates upon an extended heat-treatment. Presently a model governing the oxidation and reduction kinetics of donor-defects is applied to describe the observed temperature dependence. Quantified by the change in the saturated turn-on voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{{\text {ON}\text {Sa}\text {t}}}$ </tex-math></inline-formula> ), the parallel shift of the transfer characteristic of a TFT after an extended oxidizing heat-treatment in the temperature range from 300 to 450 °C can be precisely predicted by measurable model parameters. These results further illustrate the utility of the model as a tool for developing and optimizing MO TFT technologies by controlling <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {V}_{{\text {ON}\text {Sa}\text {t}}}$ </tex-math></inline-formula> .

A Compact Low-Voltage D-type Flip Flop Using Oxide TFTs and Its Application in Sequential Circuits

This brief presents a low-voltage D-type flip flop (D-FF) and its application in the sequential circuits, namely shift register (SR) and counter. These circuits were fabricated on a 30 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thick polymide substrate using single-gate indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). The proposed D-FF is designed using only 18 n-type transistors. This circuit has shown almost 100% improvement in frequency of operation compared to state-of-the-artwork from measurements at a low power supply voltage of 4V. In addition, the resulting 6-bit SR and 6-bit counter show expected functionality with the proposed D-FF. These circuits would find potential applications in display drivers and flexible smart sensing systems.

Performance of Transparent Indium–Gallium–Zinc Oxide Thin Film Transistor Prepared by All Plasma Enhanced Atomic Layer Deposition

Transparent indium–gallium–zinc oxide thin film transistor (IGZO-TFT) prepared by all plasma enhanced atomic layer deposition (PEALD) has been firstly investigated. As the chemical composition has a considerable impact on the performance of IGZO TFTs, the properties of IGZO film and IGZO-TFT based on different In2O3 cycle ratios are investigated. The IGZO film prepared by PEALD shows amorphous state with excellent conformity and uniformity. Moreover, the a-IGZO films with different In2O3 cycle ratios are applied to TFT fabrication. When the a-IGZO thin film with 35% In2O3 cycle ratios, the transistor presents satisfactory electrical performance with a threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> ) of 1.7 V, a saturation mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\text {sat}}$ </tex-math></inline-formula> ) of 8.8 cm2/Vs, a subthreshold swing (SS) of 0.2 V/decade and an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{ON}/\text{I}_{OFF}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.2\times 10^{{8}}$ </tex-math></inline-formula> . This work provides a new way to achieve transparent TFT which better for practical commercial applications.

Effects of Oxygen Content on Output Characteristics of IGZO TFTs under High Current Driving Conditions

We study the effects of oxygen content in indium-gallium-zinc oxide (IGZO) thin films on the output characteristics of IGZO thin-film transistors (TFTs) under high current driving conditions. Output curves were characterized at a high gate-to-source voltage (= 40 V) from both oxygen-rich and oxygen-poor IGZO TFTs. Characterization results showed that the drain current (ID) decreased with an increase in the drain-to-source voltage (VDS) under high-VDS conditions in the oxygen-rich IGZO TFTs, but abruptly increased with VDS in the oxygen-poor IGZO TFTs. From the detailed analysis of the transfer and capacitance-voltage curves obtained after output curve characterization by varying the VDS sweep range, the abnormal behavior of the output curves was mainly attributed to the increased number of trapped electrons within the gate dielectric and that of the doubly ionized oxygen vacancies in IGZO during the output curve characterization at high VDSs in oxygen-rich and oxygen-poor IGZO TFTs, respectively. The abnormality of the output curve was more significant in a wider channel device in both TFTs, which was attributed to the increased device temperature due to the self-heating effects.

Quantitative Analysis of Channel Width Effects on Electrical Performance Degradation of Top-gate Self-aligned Coplanar IGZO Thin-film Transistors under Self-heating Stresses

In this study, a quantitative analysis was conducted on the effects of channel width on electrical performance degradation induced by self-heating stress (SHS) in top-gate self-aligned coplanar indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). From the transfer and capacitance-voltage curves obtained before and after SHS, we revealed that the electrical performance of the TFT was nonuniformly degraded along the channel length direction and the degree of this degradation was more significant in TFTs with a wider channel width. The threshold voltage shift (ΔVSUBTH/SUB) under SHS in the fabricated IGZO TFT was mainly attributed to the increase in the density of shallow donor states and acceptor-like deep states in the IGZO active region and electron trapping into the fast and slow traps in the SiOSUBX/SUB gate dielectric. In addition, we conducted a decomposition of the SHS-induced ΔVSUBTH/SUB originated from each degradation mechanism using the subgap density of states-based ΔVSUBTH/SUB decomposition technique for TFTs with different channel widths. Although every ΔVSUBTH/SUB from each degradation mechanism increased as the channel width increased, increased electron trapping into the slow trap in the SiOSUBX/SUB gate dielectric was the dominant reason for the larger ΔVSUBTH/SUB under SHS in IGZO TFTs with a wider channel width.

High-Performance Photodetector with a-IGZO/PbS Quantum Dots Heterojunction

Low cost, high absorption coefficient, tunable band gap, and compatibility with flexible devices make lead sulfide (PbS) quantum dots (QDs) based photoconductors promising candidates for next-generation near-infrared (NIR) photodetectors. However, the detection performance of PbS QDs-based photoconductors still needs to be further improved, because there is a trade-off among the responsivity/detectivity/bandwidth in the device development process, that is, it is difficult to improve the three parameters simultaneously. Inspired by the design idea of sensitized phototransistor, a kind of amorphous indium gallium zinc oxide (a-IGZO)/PbS QDs heterojunction photoconductor is reported in this paper. The most prominent feature of this work is that a-IGZO, like a photocurrent “amplifier”, increases the photocurrent by several orders of magnitude without generating additional noise, and thus improves the sensitivity and responsiveness of the device. Compared with the initial pure PbS QDs-based photoconductor, the heterojunction device is able to increase the photocurrent by 3000 times together with a low dark current, and improve the response speed of the device with the help of interface-assisted carrier separation and recombination. In the NIR band, the device exhibits an exciting performance with a detectivity of 1.53 × 1013 Jones, a responsivity of 19070 mA/W and a decay time of 0.39 ms, respectively. By applying the a-IGZO/PbS QDs heterojunction to paper-based devices, a flexible device with bending resistance can be obtained, and the detection performance of the device does not deteriorate after 1000 times of bending.

An extensive study on multiple ETL and HTL layers to design and simulation of high-performance lead-free CsSnCl3-based perovskite solar cells

Cesium tin chloride (CsSnCl3) is a potential and competitive absorber material for lead-free perovskite solar cells (PSCs). The full potential of CsSnCl3 not yet been realized owing to the possible challenges of defect-free device fabrication, non-optimized alignment of the electron transport layer (ETL), hole transport layer (HTL), and the favorable device configuration. In this work, we proposed several CsSnCl3-based solar cell (SC) configurations using one dimensional solar cell capacitance simulator (SCAPS-1D) with different competent ETLs like indium–gallium–zinc–oxide (IGZO), tin-dioxide (SnO2), tungsten disulfide (WS2), ceric dioxide (CeO2), titanium dioxide (TiO2), zinc oxide (ZnO), C60, PCBM, and HTLs of cuprous oxide (Cu2O), cupric oxide (CuO), nickel oxide (NiO), vanadium oxide (V2O5), copper iodide (CuI), CuSCN, CuSbS2, Spiro MeOTAD, CBTS, CFTS, P3HT, PEDOT:PSS. Simulation results revealed that ZnO, TiO2, IGZO, WS2, PCBM, and C60 ETLs-based halide perovskites with ITO/ETLs/CsSnCl3/CBTS/Au heterostructure exhibited outstanding photoconversion efficiency retaining nearest photovoltaic parameters values among 96 different configurations. Further, for the six best-performing configurations, the effect of the CsSnCl3 absorber and ETL thickness, series and shunt resistance, working temperature, impact of capacitance, Mott–Schottky, generation and recombination rate, current–voltage properties, and quantum efficiency on performance were assessed. We found that ETLs like TiO2, ZnO, and IGZO, with CBTS HTL can act as outstanding materials for the fabrication of CsSnCl3-based high efficiency (η ≥ 22%) heterojunction SCs with ITO/ETL/CsSnCl3/CBTS/Au structure. The simulation results obtained by the SCAPS-1D for the best six CsSnCl3-perovskites SC configurations were compared by the wxAMPS (widget provided analysis of microelectronic and photonic structures) tool for further validation. Furthermore, the structural, optical and electronic properties along with electron charge density, and Fermi surface of the CsSnCl3 perovskite absorber layer were computed and analyzed using first-principle calculations based on density functional theory. Thus, this in-depth simulation paves a constructive research avenue to fabricate cost-effective, high-efficiency, and lead-free CsSnCl3 perovskite-based high-performance SCs for a lead-free green and pollution-free environment.

An Analytical Surface Potential and Effective Charge Density Approach Based Drain Current Model for Amorphous InGaZnO Thin-Film Transistors

An analytical surface-potential-based drain current model for amorphous indium–gallium–zinc–oxide (a-InGaZnO) thin film transistors (TFTs) is proposed by introducing an effective charge density approach in this paper. This approach gives two initial approximate values of the effective state density and the effective thermal voltage by using the dominant state of the free charge density in total charge density, and then obtains a high-precision one-exponent equivalent transformation for three-exponent total charge density. Based on this approach, we have solved the problem that the physical meaning of the transition area in the regional method is not clear and a one-piece analytical surface potential solution to Poisson’s equation is successfully derived. Furthermore, the drain current is also explicitly derived from the charge sheet model and I-V characteristics of a-InGaZnO TFTs are reproduced from the above obtained model. Finally, accurate and effective surface-potential model and drain current model are obtained and verified by experimental data, respectively. Good verification results prove that the proposed model could become an accurate and suitable tool for being embedded into a circuit simulation.

Cu2O p-type Thin-Film Transistors with Enhanced Switching Characteristics for CMOS Logic Circuit by Controlling Deposition Condition and Annealing in the N2 Atmosphere

Cuprous oxide (Cu2O) p-type thin-film transistors (TFTs) can be practically applied for complementary metal oxide semiconductor (CMOS) logic circuits, but the electrical performances are still insufficient due to high off-current and low field-effect mobility. Here, we have demonstrated Cu2O TFTs with improved field-effect mobility and low off-current through reduction of cupric oxide (CuO) impurities and dissociative Cu defects with the combination of deposition and annealing conditions. Copper oxide was deposited by radio frequency sputtering in mixed gases of argon and oxygen. After that, the deposited copper oxide was annealed at 800 °C in the tube furnace under a N2 atmosphere instead of a high vacuum condition. The fabricated Cu2O thin film had a high crystalline quality, the ratio of dissociative Cu defects decreased from 11.3 to 3.1%, and the electrical performances of the TFT including the fabricated Cu2O thin film exhibited the field-effect mobility of 1.11 ± 0.05 cm2/V·s, the on/off current ratio of 4.68 ± 0.8 × 104, and the subthreshold swing value of 3.91 ± 0.21 V dec–1. The fabricated Cu2O TFT showed a Vth shift of 3.31 V in the transfer curve under negative bias stress. Nitrogen plays a role in promoting Cu2O phase formation while it prevents CuO phase formation during the annealing process. In addition, oxygen added during sputtering increases the ratio of CuO in the copper oxide thin film and works effectively to reduce dissociative Cu defects in the annealing process. To determine the feasibility of the CMOS logic circuit, we also demonstrated the inverter with n-type indium–gallium–zinc oxide (IGZO) TFT and p-type Cu2O TFT, which showed a voltage gain of 14 at VDD = 20 V.

High-Performance 1-V IGZO Thin-Film Transistors Gated With Aqueous and Organic Electrolyte-Anodized Al x O y

In this work, ultrathin AlxOy films used as gate dielectrics in thin-film transistors (TFTs) are prepared in aqueous and organic electrolytes using an anodization process. A series of anodization voltages are used to investigate the effects of anodization electrolyte on the surface morphologies and electrical properties of AlxOy films. By using such anodized AlxOy films as gate dielectrics, 1-V indium–gallium–zinc–oxide (IGZO) TFTs are fabricated. The electrical characteristics of the IGZO TFTs with AlxOy films prepared in organic electrolyte are enhanced in comparison with those of the IGZO TFTs with AlxOy films prepared in aqueous electrolyte. The enhancement may be due to more carbon species introduced to the anodized dielectric films. This work offers a method to further improve the properties of ultrathin anodized dielectrics and shows the potential of using anodization in the future for large-area low-power electronics.

Nanodiodes on a Digestible Substrate

Biodegradable and edible electronics will need electronic components for signal modulation and wireless communication; hence, non-linear and high frequency components will be required. Here, a method to fabricate nanodiodes on isomalt (a sugar substitute) substrates is reported. Coplanar electrodes of Al and Au with nanogap separation were fabricated on top of isomalt through design of an adhesion lithography process specifically to accommodate the low melting point and high solubility of the substrate. Lateral diodes with rectification ratios of 103 were created by depositing indium gallium zinc oxide (IGZO) using a target with an atomic ratio of In2O3:Ga2O3:ZnO (1:1:1) on top of the electrodes without an annealing step.

Electrical Reliability of Flexible Low-Temperature Polycrystalline Oxide Thin-Film Transistors Under Mechanical Stress

Electronic devices based on flexible displays have been developed for use in various applications. Upon bending such devices, the applied mechanical force deteriorates the reliability of the devices. Therefore, a high bending reliability that is influenced by tensile and compressive forces that vary depending on the bending radius of curvature must be secured to ensure a reliable device operation. In this study, we investigated the electrical characteristics of flexible low-temperature polycrystalline silicon (LTPS) and amorphous indium–gallium–zinc–oxide (a-IGZO) thin-film transistors (TFTs) on polyimide (PI) substrate and subsequently conducted reliability evaluation of the devices under mechanical stress by applying negative bias temperature illumination stress (NBTIS). The degradations in the electrical properties, such as threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> ) shift, OFF-state current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {off}}$ </tex-math></inline-formula> ), and subthreshold slope (SS), and reliability, increased, and the reliability worsened, as the tensile force increased under decreasing radius of curvature, whereas relatively low degradation occurred under compressive force. A tensile stress-induced increase in grain boundary state density in polycrystalline silicon (poly-Si) and oxygen vacancy in a-IGZO were verified by density of state (DOS) extraction; the cracks occurring due to tensile stress were optically analyzed; the external moisture penetration along the cracks further degrades the device characteristics. This study provides an analysis of device design for ensuring reliability under the application of mechanical stress, thereby contributing to the development of reliable flexible technology.

Amorphous indium–gallium–zinc–oxide memristor arrays for parallel true random number generators

True random number generators (TRNGs) can generate unpredictable binary bitstream by exploiting the intrinsic stochasticity in physical variables. In a threshold switching memristor, the stochastic forming/rupture of conducting pathway has been proved to be a good random source, while further improvement of high randomness and throughput is still a challenge. Here, a crossbar array of amorphous indium–gallium–zinc–oxide (a-IGZO)-based threshold switching memristors was designed for high-throughput TRNGs. The intrinsic stochasticity of Ag conductive filament in IGZO memristor and the stochastic sneak paths in the crossbar array are the two sources of randomness in our TRNGs. In our design, one input pulse train can produce multi-channel random bits, which enables a high scalability for such TRNGs. In addition, the average energy consumption of the TRNGs can be further reduced by increasing the integration scale of the memristors. Such IGZO-based TRNGs are of great significance for security applications.

Reservoir computing based on electric-double-layer coupled InGaZnO artificial synapse

Physical reservoir computing (PRC) is thought to be a potential low training-cost temporal processing platform, which has been explored by the nonlinear and volatile dynamics of materials. An electric-double-layer (EDL) formed at the interface between a semiconductor and an electrolyte provided a great potential for building high energy-efficiency PRC. In this Letter, EDL coupled indium-gallium-zinc-oxide (IGZO) artificial synapses are used to implement reservoir computing (RC). Rich reservoir states can be obtained based the ionic relaxation-based time multiplexing mask process. Such an IGZO-based RC device exhibits nonlinearity, fade memory properties, and a low average power of ∼9.3 nW, well matching the requirement of a high energy-efficiency RC system. Recognition of handwritten digit and spoken-digit signals is simulated with an energy consumption per reservoir state of ∼1.9 nJ, and maximum accuracy of 90.86% and 100% can be achieved, respectively. Our results show a great potential of exploiting such EDL coupling for realizing a physical reservoir that would underlie a next-generation machine learning platform with a lightweight hardware structure.

Field-Effect Mobility Extraction of Solution-Processed InGaZnO Thin-Film Transistors Considering Dielectric Dispersion Behavior of AlOx Gate Insulator

We investigated the effect of the dielectric dispersion behavior of solution-processed aluminum oxide (AlOx) on the field-effect mobility estimation of the solution-processed indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs). In the metal–insulator–metal (MIM) structure, solution-processed AlOx dielectric film annealed at 350 °C showed dielectric dispersion behavior, which was attributed to the electric double layer (EDL) due to the mobile ions, such as a hydrogen ion (H+) or a hydroxyl group (OH–). The annealing process at a higher temperature of 500 °C reduced the number of mobile ions in the AlOx film and removed the dielectric dispersion behavior in the MIM structure. However, solution-processed IGZO TFTs using the AlOx annealed at 500 °C as gate insulator showed dielectric dispersion-related behavior. We found that the chemical reaction to form a solution-processed IGZO layer supplied the mobile ions to the AlOx film, resulting in the EDL and dielectric dispersion phenomenon. Therefore, the dielectric dispersion should be investigated in the metal–insulator–semiconductor–metal structure, although the dispersive behavior does not occur in the MIM structure. Furthermore, the field-effect mobility (μFE) of solution-processed IGZO TFTs was 35.6 and 17.5 cm2/V·s with and without consideration of the dielectric dispersion behavior. The μFE was overestimated by 203% without regard to the dielectric dispersion. Consequently, the dielectric dispersion should be considered to estimate the accurate μFE of solution-processed IGZO TFTs with solution-processed AlOx as the gate insulator layer.

Facile preparation of fully amorphous bulk PbO-Ga2O3 system for direct photon-charge conversion X-ray detector with low dark current and high photocurrent

An amorphous state makes the material free of interface and ensures the overall uniformity of the material and device, to the benefit of large-area electronic devices, such as amorphous silicon and indium gallium zinc oxide display devices and amorphous selenium flat panel detectors. Elements with high atomic number endow the PbO-Ga2O3 system materials with high X-ray absorption coefficients, and wide band gap leading to a low dark current and high signal-to-noise ratio. These advantages are in line with the criteria for a practical X-ray detector development. Herein, the direct photon-charge conversion X-ray detectors based on fully amorphous bulk PbO-Ga2O3 system [(PbO)x(Ga2O3)1-x (x = 0.698, 0.747, 0.761, 0.789)] was fabricated by using high-temperature melt quenching method. Under a fixed electric field of 100 V/mm and X-ray irradiation dose rate of 0.57 μGy ms−1, the dark current as low as 1.1 pA mm−2, photocurrent up to 1600 pA mm−2, signal-to-noise ratio up to 800, comparable sensitivity as 2.02 μC Gy−1 cm−2 of the as fabricated X-ray detector were obtained. All the results suggest that amorphous bulk PbO-Ga2O3 system materials are potential candidates for developing of direct photon-charge conversion X-ray detectors.